By Susan Milius
Fiddler crabs will do battle to help a punier rival, a report in the May American Naturalist concludes. But it isn’t out of kindness.
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Ecologists already knew that male fiddler crabs will sometimes take on an attacker who is trying to invade a neighbor’s territory. By setting up a series of bouts between crabs of the species Uca annulipes on a beach in Mozambique, Australian researchers have found that the crustaceans defend only smaller neighbors. And they do so only when an intruder is intermediate in size between their neighbor and themselves.
Size has a lot to do with which crab is going to win a fight. So the rules of crab engagement suggest it’s not a mutual defense pact that motivates a male to defend his neighbor. By the rules, the little guy next door isn’t going to help his big defender. But the big guy still benefits by preventing a larger rival from moving in next door and instigating the customary series of border clashes, said study coauthor Michael Jennions of Australian National University in Canberra.